Increasing concerns about the impact of the internal combustion engine on global warming are putting added pressures on the automotive industry to develop more environmentally friendly engines. Generally, the approach is to increase the efficiency of the engine while reducing the displacement in efforts to bum less fuel thereby reducing emissions. This small displacement engine would be used as a stand alone power plant or as the principal source of power in an electric hybrid configuration. Currently, the most promising candidate is to take the most efficient internal combustion engine, the direct-injection (DI) diesel, and reduce its' displacement to as small as operationally possible. Due to minimal power requirements demanded by consumers, the required displacement to produce acceptable output with present technology will be at least 1.0 liters.
Four major concerns are associated with the use of diesel technology in the personal-use vehicle market. First, consumer acceptance of diesels has been mitigated by the noise, vibration and harshness (NVH) associated with diesel operation. Second, the power to weight ratio tends to decrease with decreasing displacement. The latter difficulty is due to the lack of direct proportionate component reduction in size or weight as displacement is reduced. Examples of this are the inability to reduce components such as cast wall thickness, injection systems, superchargers, etc. at the same scale as the displacement. Third, compounding this problem is the related difficulty of maintaining the same air transporting capacity as with larger displacements due the inability to proportionally scale components such as valve stems, injectors and glow plugs. Finally, reducing cylinder displacements reduces thermal efficiency due to reduced combustion chamber surface-to-volume ratio.
While the rotary valve engine in my co-pending application Ser. No. 08/714,591 (which is incorporated herein by reference) can use various fuels, it is particularly well suited for small cylinder diesel operation. This Rotary Valve Diesel (RVD) addresses the principal concerns listed above. With respect to the preferred embodiment of four cylinders, the RVD uses short, twin, opposed revolution, lightweight crankshafts with crank throws located 180 degrees apart from the adjacent crankthrow. This arrangement with other elements described later, greatly reduces the NVH of this engine. Second, the compact size of the engine along with the lightweight cranks reduce the weight of the RVD. Third, the size of the intake and exhaust valve openings, as well as the intake and exhaust passages all can be at least four times the size of the corresponding elements of conventional poppet valve engines. Not only does this greatly increase the pumping efficiency of the RVD, but also dramatically increases the air transport capacity of the engine as well. This increased transport capacity can be used to literally double the RPMs. The RVD can double the RPMs due to new developments in injector technology; conventional diesel engines have maximum RPM levels of 34000 RPMs; and the stroke of the RVD is short. The combination of these factors allow the doubling of RPMs without exceeding critical engine sliding speeds. In applications where high performance is more critical than engine life, the RVD has enough transport capacity to more than triple RPMs.
The RVD also increases engine thermal efficiency. Efficiency gains are possible because the large valve openings allow the power stroke to be lengthened, the valve of the RVD reduces heat losses because the same portions of the valve are always exposed to the same combustion cycle, and fins located in the exhaust valve transmit power back to the crankshaft. With increased RPMs and gains in both the thermal and pumping efficiencies, the RVD can reach unprecedented power to weight ratios in piston engine technology.